Fluid catalytic cracking (FCC) is a well-known process for the conversion of relatively high boiling point hydrocarbons to lighter boiling hydrocarbons in the heating oil or gasoline (or lighter) range. Such processes are commonly referred to in the art as “upgrading” processes, and “FCC” as referred to herein encompasses conventional FCC processes and residual FCC processes. To conduct FCC processes, FCC units are generally provided with one or more reaction chambers. A hydrocarbon stream is typically contacted in the one or more reaction chambers with a particulate cracking catalyst that is maintained in a fluidized state under conditions that are suitable for the conversion of relatively high boiling point hydrocarbons to lighter boiling hydrocarbons.
Typically, the lighter boiling hydrocarbons are withdrawn from the FCC unit as an offgas stream, which is separated into various intermediate and product hydrocarbon streams in an FCC main column. A fraction that remains in vapor form from the FCC main column is taken as a main column overhead stream and fed to an overhead receiver, where liquid fractions and a residual vapor stream are separated. The residual vapor stream is compressed to form a pressurized stream in preparation for further separation of components therefrom. In particular, the pressurized stream is generally fed to a high pressure receiver, which separates the pressurized stream into one or more liquid streams and a high pressure vapor stream. It is generally desirable to separate C3+ hydrocarbons from the high pressure vapor stream, and such separation is often conducted through liquid-vapor phase absorption in a primary absorber. As referred to herein, “CX” means hydrocarbon molecules that have “X” number of carbon atoms, CX+ means hydrocarbon molecules that have “X” and/or more than “X” number of carbon atoms, and CX− means hydrocarbon molecules that have “X” and/or fewer than “X” number of carbon atoms.
To separate C3+ hydrocarbons from the high pressure vapor stream, a stabilized and/or unstabilized gasoline stream is often employed as a liquid absorption stream in the primary absorber. The stabilized gasoline stream is generally derived from the high pressure vapor stream and may be provided from a debutanizer column after separation of C4− hydrocarbons. The unstabilized gasoline stream contains C4+ hydrocarbons and is generally derived from the main column overhead stream as a liquid stream provided from the overhead receiver. A high flow rate of the stabilized and/or unstabilized gasoline streams is often required to effectively separate the C3+ hydrocarbons in the primary absorber, which impacts capital and operating expenses associated with separation of C3+ hydrocarbons from the high pressure vapor stream.
Accordingly, it is desirable to provide hydrocarbon processing apparatuses and methods of refining hydrocarbons with minimized flow rate of stabilized and/or unstabilized gasoline streams during absorptive separation of C3+ hydrocarbons from the high pressure vapor stream. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.